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doi:10.2204/iodp.proc.338.102.2014

Physical properties

Physical properties measurements provide crucial parameters for characterization of consolidation state and deformation of rock formations and are an important tool for integrating cores, cuttings materials, and LWD data. In addition, physical properties are indicators of composition and environmental conditions and are essential for stratigraphic correlation (Blum, 1997), flow properties evaluation, and formation evaluation.

Whole-round sections from cored intervals were first scanned by X-ray CT and then thermally equilibrated at room temperature for ~3 h before any physical properties measurements were conducted. Nondestructive measurements on the whole-round sections included gamma ray attenuation (GRA) density, magnetic susceptibility, NGR, ultrasonic P-wave velocity, and noncontact electrical resistivity (NCR) using the MSCL-W (Geotek Ltd., London, United Kingdom). For soft-sediment cores, thermal conductivity was measured on whole-round sections using a full-space needle probe before cores were split into archive and working halves. For cores with highly consolidated or lithified sediment, nondestructive thermal conductivity was measured using a half-space line source. Electrical resistivity was measured using a Wenner array of electrodes on working halves of soft sediment, and both electrical resistivity and P-wave velocity measurements were conducted on discrete samples of consolidated sediment from working halves. MAD measurements were performed on discrete samples from working halves and cuttings. High-resolution digital image photography and color reflectance measurements were performed on archive halves using the MSCL-I and MSCL-C.

For cuttings recovered from Hole C0002F (875.5–2004.5 mbsf), limited measurements were conducted because of the amount of the available material. Unwashed cuttings were analyzed for NGR using the MSCL-W to determine variations in the radioactive counts of the samples and for correlation with LWD gamma ray measurements. Cuttings were rinsed with seawater to remove contamination from drilling mud and sieved into 0.25–1 mm, 1–4 mm, and >4 mm size fractions (see also “Lithology”). Washed cuttings samples (~40 cm³ total volume) were taken from the 1–4 mm size fraction and samples smaller than 8 mm were hand-picked from the >4 mm fraction for physical properties measurements, including MAD, magnetic susceptibility measurements, and dielectrics and electrical conductivity.

MSCL-W (cores and cuttings)

WRCs were scanned as the core section passed through the MSCL-W. Unwashed bulk cuttings for NGR analysis were packed into a 12 cm long core liner, producing a volume of 400 cm³, and measured by the MSCL-W NGR unit.

Gamma ray attenuation density

A well-collimated gamma ray beam (primary photon energy of 662 keV) is produced by a small (370 MBq) ¹³⁷Cs source. The gamma ray intensity of the beam is measured across the core with a scintillation detector that is composed of a scintillation crystal and an integrated photomultiplier tube. The first-order mechanism for GRA is inelastic scattering by electrons, resulting in a partial energy loss (Compton effect). Because it is directly related to electron density, bulk density (ρ_b) can be determined from the amount of attenuation by

where

• µ = Compton attenuation coefficient,
• d = sample thickness or outer liner diameter,
• I₀ = gamma source intensity, and
• I = measured intensity through the sample.

Accordingly, the GRA method can provide information about bulk rock density by measuring the attenuation of a gamma ray beam that passes through a core. Here, an empirical approach is used to relate bulk density and GRA. The system is calibrated with a special sealed calibration “core section,” composed of a set of aligned aluminum cylinders of various diameters surrounded by distilled water in a sealed core liner. Density (ρ) depends on the diameter of the aluminum cylinder and spans from ρ = 1 g/cm³ (water only) to 2.71 g/cm³ (aluminum only). For the calibration measurement, gamma ray counts were taken for each aluminum cylinder for a count time of 60 s. The resulting ln(I) was plotted against the product of the known parameters ρ and d of the calibration core section and fitted with a regression line of the following type:

where d is the internal diameter of the liner and A, B, and C are coefficients determined from the polynomial equation fit. Density measurements on core samples were conducted perpendicular to the core axis every 4 cm. The gamma source collimator is 5 mm in diameter, so each data point reflects the properties of the surrounding 5 mm interval, corresponding to a maximum volume of investigation of ~15.6 cm³.

P-wave velocity

Ultrasonic P-wave velocity (V_P) was measured for WRCs by measuring distance between sondes or outer liner diameter (d) and traveltime (t₀):

A linear variable differential transformer, used to measure the outer liner diameter, is integrated with a 500 kHz P-wave transmitter/receiver system. The system is mounted horizontally on the MSCL-W and measures d and t₀ perpendicular to core axis at a 4 cm interval. The measured traveltime (t₀) between the transducers is delayed by the pulse traveltime through the liner, the threshold peak detection procedure, and the pulse travel between transducers and the electronic circuitry. Traveltime is corrected for these parameters by calibrating the system using a core liner filled with pure water, which has a known P-wave velocity (1480 m/s at 20°C). The corrected P-wave velocity through the core (V_core) (m/s) is

where

• W = total wall thickness of the core liner,
• t_w = measured traveltime through the water-filled
  calibration liner, and
• V_w = known P-wave velocity of pure water at room
  temperature.

Noncontact electrical resistivity

Bulk electrical resistivity is controlled by solid grain and interstitial water resistivity. Therefore, it provides information about other sediment physical properties such as porosity, tortuosity, permeability, and thermal conductivity. The bulk electrical resistivity (R_e) is defined by the electrical resistance (R) and the geometry of the core measured:

where

• L = distance between the electrodes, and
• A = cross-sectional area of the core.

The ratio between the bulk electrical resistivity and the resistivity of the pore fluid (R_f) alone gives the apparent formation factor (F_a) (Archie, 1947):

Whereas the true formation factor (F = τ²/ϕ_c) is a function of the true tortuosity (τ) of the fluid flow path and the connected porosity (ϕ_c), F_a includes the effect of grain-surface conductivity.

For bulk resistivity measurements, the MSCL-W is equipped with a noncontact resistivity sensor that operates by inducing a high-frequency magnetic field in the core using a transmitter coil. The magnetic field induces electrical currents in the core that are inversely proportional to the resistivity. Very small magnetic fields are created in the core by the induced electrical currents and are measured by a receiver coil. To measure these magnetic fields accurately, readings generated from the measuring coils are compared to readings from an identical set of coils operating in air. Calibration is achieved by filling short lengths of core liner with water of known NaCl concentrations to provide a series of calibration samples with known resistivities that are logged on the MSCL-W. A power law calibration equation is found by fitting averaged values of NCR output and corresponding resistivities of the known standards. Electrical resistivity data were obtained at 4 cm intervals along each core section.

Magnetic susceptibility

Magnetic susceptibility is the degree to which a material can be magnetized by an external magnetic field. Magnetic susceptibility was measured with a Bartington Instrument MS2C system with an 8 cm diameter loop sensor on the MSCL-W. A nonsaturating, low-intensity alternating magnetic field (8.0 × 10^–4 mA/m root mean square at 0.565 kHz) is produced by an oscillator circuit in the sensor. Any material near the sensor that has a magnetic susceptibility causes a change in the oscillator frequency. This pulse frequency is then converted into a magnetic susceptibility value. With a reference piece of known magnetic susceptibility, the long-term consistency of the calibration is checked regularly. The spatial resolution of the loop sensor is ~4 cm, with an accuracy of 5%. Magnetic susceptibility data were obtained at 4 cm intervals with an acquisition time of 1 s.

Natural gamma radiation

NGR emissions were measured on all core sections and unwashed cuttings samples to determine variations in the radioactive counts. The NGR system records radioactive decays of long-period isotopes ⁴⁰K, ²³²Th, and ²³⁸U in a lead-shielded detector unit. The unit is composed of a scintillator, which is coupled to a photomultiplier tube and connected to a bias base that supplies high-voltage power and a signal preamplifier. Two horizontal and two vertical detection units were mounted in a lead cube-shaped housing around the core. NGR was measured every 16 cm for 30 s on core sections with a resolution of ~16 cm.

We also measured the NGR of unwashed cuttings packed in a 12 cm long core liner. Background radiation noise was determined as 34.0 cps by measuring the same size liner filled with distilled water. Two standard radioactive isotopes with known gamma ray emission energies (¹³³Ba and ⁶⁰Co) were used for the energy calibration and adjustment of the spectral detection windows.

P-wave velocity measurements on MSCL-S (cores)

Ultrasonic P-wave velocity was measured on working-half core sections with the split core multisensor core logger (MSCL-S) in addition to the MSCL-W measurements. V_P measurements were conducted every 4 cm on selected sections from Site C0022 (see “Physical properties” in the “Site C0022” chapter [Strasser et al., 2014c]). The measurement procedures are the same as the MSCL-W V_P measurements discussed above.

Magnetic susceptibility (washed cuttings)

For magnetic susceptibility analysis, ~10 cm³ of seawater-rinsed cuttings was taken from vacuum-dried cuttings from the 1–4 mm and the >4 mm size fractions and placed into a preweighed paleomagnetic (pmag) cube. The prepared cube, with a volume of 7 cm³, was then analyzed with the Kappabridge KLY 3S system (AGICO, Inc.). Sensitivity for the measurement is 3 × 10^–8 SI, and intensity and frequency of the field applied are 300 mA/m and 875 Hz, respectively. A standard was measured once a day to ensure long-term quality of the system calibration. A blank empty cube was measured for each continuous series of experiments to determine background impact. Samples were then measured using standard test procedures.

Thermal conductivity (cores)

Thermal conductivity was measured on the working halves at a spacing of at least 1 measurement per core using either a half-space line source probe (HLQ probe; for consolidated cores from Holes C0002H and C0002J and below 337 mbsf in Hole C0022B) or a full-space needle probe (for soft-sediment cores from Holes C0002K, C0002L, and C0021B and above 368 mbsf in Hole C0022B) and a high-precision thermal conductivity meter (TeKa TK04 unit) (Von Herzen and Maxwell, 1959; Vacquier, 1985). For consolidated cores, a representative ~10 cm long piece from the working half was soaked in a seawater bath at ambient temperature (20°C) for at least 15 min before measurement. The HLQ probe was placed on the flat surface of the specimen with the line probe oriented parallel to the core axis. For soft-sediment cores, the full-space probe was inserted into whole-round sections through a hole drilled through the working-half side of the core liner.

For all thermal conductivity measurements, the measurement started automatically when the monitored temperature in the sample ensured that thermal drift was <0.4 mK/min (typically within 1–2 min). During measurement, a calibrated heat source was applied and the rise in temperature was recorded for ~80 s. Thermal conductivity values were based on the observed rise in temperature for a given quantity of heat supplied. Long-term quality of tools and data was validated by a daily calibration on standard Macor samples with known thermal conductivity (1.652 W/[m·K] ± 2% for consolidated cores, 1.623 W/[m·K] ± 2% for soft cores).

Moisture and density measurements (cores and cuttings)

The purpose of MAD measurements is to obtain general physical properties of sediment or rock specimens such as bulk wet density, bulk dry density, grain density, water content, porosity, and void ratio. All the properties can be calculated using phase relations based on direct measurements of wet sample mass (M_wet), dry sample mass (M_dry), and dry sample volume (V_dry) (Noorany, 1984). Standard seawater density (ρ_f = 1.024 g/cm³) and salinity (s = 3.5%) are assumed for the phase relations. All the phase relations are based on the assumption that interstitial water fills the pores. For calculation of each physical property, IODP Method C (Blum, 1997) was used for both core samples and cuttings. There is no difference in measurements and calculations between the two sample types, only in sample preparation.

Sample preparation

Core samples

Two MAD samples (~5 cm³ each) were taken per core section from either the working half or the “cluster” samples adjacent to whole-round samples. Disturbed parts of core were avoided for sample location. Special care was taken to avoid drilling mud in MAD samples.

Cuttings

Cuttings samples were taken at 5–10 m depth intervals of drilling progress for MAD measurement. After rinsing with seawater, the cuttings of the working portion were segregated into three size fractions (0.25–1 mm, 1–4 mm, and >4 mm) by sieving. A volume of ~20 cm³ taken from the 1–4 mm size fraction was used for MAD measurements. Hand-picked pieces from the >4 mm size fraction were also used to examine the effect of fraction size on MAD results. Wet cuttings were prepared after sieving by removing excess water by gently wiping cuttings with a Kimwipe until no visible water films were observed on the cuttings surfaces. The samples were then placed into a weighed glass jar.

MAD measurements

M_wet was measured using a paired electronic balance system designed to compensate for the ship’s heave. After measurement, the wet samples were placed in a convection oven for >24 h at 105° ± 5°C to dry. The dry samples were then cooled in a desiccator for at least 1 h before dry mass and volume measurement. M_dry was determined using the paired electronic balance system. V_dry was measured using a helium-displacement Quantachrome penta-pycnometer with a nominal precision of ±0.04 cm³. An average of five measurements was reported for each sample.

Phase relations in marine sediment

From the direct measurements of M_wet, M_dry, and V_dry, pore fluid mass (M_f), salt mass (M_salt), mass of solids excluding salt (M_s), pore fluid volume (V_f), salt volume (V_salt), and volume of solids excluding salt (V_s) can be obtained by

and

where

• M_wet = total mass of the wet sample,
• M_dry = mass of the dried sample,
• s = salinity (3.5%),
• ρ_f = density of pore fluid (1.024 g/cm³), and
• ρ_salt = density of salt (2.220 g/cm³).

Calculations of physical properties

Water content (W_c) was determined following the methods of the American Society for Testing and Materials (ASTM) designation D2216 (ASTM International, 1990). Corrections are required for salt when measuring the water content of marine samples. In addition to the recommended water content calculation in ASTM D2216 (i.e., the ratio of pore fluid mass to dry sediment mass as percent dry weight), we also calculated the ratio of pore fluid mass to total sample mass (percent wet weight). The equations for water content are

and

Bulk density (ρ_b), dry density (ρ_d), and grain density (ρ_g) are defined as

and

where V_wet is the bulk volume of wet sample determined from V_dry, V_f, and V_salt.

Porosity (ϕ) is given by

and reported as percentage here (ϕ[%] = ϕ × 100). Void ratio (e) is obtained by

Void ratio can also be obtained from ϕ:

Dielectrics and electrical conductivity (washed cuttings)

Dielectric constant (ε_r), which is also called relative permittivity, is a measure of the electrical polarizability of a material (Von Hippel, 1954), whereas the electrical conductivity (σ) is the inverse of electrical resistivity. When a sample is placed in an electric field, the charge carriers within the sample may undergo a translational path through the sample (electrical conduction, in S/m) or undergo temporary displacement and/or reorientation, resulting in an induced field within the sample (electrical polarization, dimensionless).

The complete dielectric versus frequency responses are governed by multiple processes that occur within the rock, from the electron scale to the pore scale (Fig. F20A), and each process (absorption and/or dissipation of energy) is characterized by the speed at which it occurs (Guéguen and Palciauskas, 1994). Resolving these multiple first-order responses over certain frequency ranges is based on the most commonly used model in dielectric spectroscopy: the Cole-Cole model (Cole and Cole, 1941), which is a modified model of the Debye approach (Debye, 1913):

where

• ε_r* = model (*) of the static permittivity or dielectric constant,
• ε_∞ = optical relative permittivity at “infinite” frequency,
• ε_S = static (S) relative permittivity,
• ω = angular frequency,
• τ = electrical relaxation time, and
• i = imaginary unit of the mathematical complex number.

In the Fourier domain, S becomes a mathematical complex number (jω) that splits the function into two members: the real (ε′_r[ω], also described as the dispersion) and imaginary (ε″_r[ω], also described as the absorption) parts that can be written in the form of

The Cole-Cole model added a smoothing parameter (α[0 – 1]) to broaden the low–high frequency transition that was often failing with the Debye model to fit to experimental data.

The Cole-Cole dielectric constant model becomes

Note that if α = 0, the Cole-Cole equation (Equation 31) is reduced to the Debye equation (Equation 29). Typical dielectric constants of water are 81 at low frequency and 1.8 at high frequency (Fig. F20B).

Sample preparation and measurement

The experimental flow is based on powdering of cuttings to manufacture a paste by adding some microfiltered Milli-Q water and using an end-load probe coaxial transmission line in contact with the prepared paste to record the dielectric and electrical conductivity over a frequency range of 30 kHz to 6 GHz.

The end-load probe coaxial transmission line dielectric measurement from the Agilent 85070E instrument is based on an inversion algorithm for the scattering parameters measured for a section of coaxial transmission line terminated against the surface of the sample (Burdette et al., 1980; Stuchly and Stuchly, 1980). It is attached to an Agilent Electronic Calibration (ECal) module (85092-60010) that is connected to a Network Analyzer 8753D from Hewlett Packard (Agilent) using a coaxial cable. A computer controls the network analyzer to start/stop measurement and records the data using an ethernet-to-USB cable attached to the ECal module. The end-load probe is a rapid measurement system, which makes it optimal for large batches of cuttings (Leung and Steig, 1992). Recent work (Josh et al., 2007, 2012) showed correlations of dielectric properties from sedimentary samples at particular frequency ranges with fluid types (movable and irreducible water), elastic properties (P-wave velocity), and some mineralogical characteristics such as specific surface area and cationic exchange capacity. These dielectric relationships indirectly evaluate the occurrence of specific clay minerals that control most of the physical properties of the samples.

The paste preparation consists of grinding the cuttings following the XRD protocol (see “X-ray diffraction”) on the seawater-washed 1–4 mm size fraction. A total of 110 samples were analyzed from Hole C0002F. An amount of 20 g of dried powder was mixed with an addition of organic particles filtered in Milli-Q water of exactly 20 mL in a centrifuge NUNC bottle. After shaking by hand for ~5 min to assure that all the salts and agglomerates were dissolved, the mixture was centrifuged at 5000 rpm for 1 h. The decanted water was transferred into a separate plastic jar to measure its salt content using the interstitial water analysis procedure (see “Geochemistry”).

The remaining cuttings paste inside the centrifuge bottle was extruded into a separate acrylic jar with known mass, kneaded gently to ensure uniformity (without excess water or trapping air bubbles), and pressed against the end-load coaxial transmission line. Four dielectric measurements were conducted at different locations on each paste sample for quality control. After measurement, the sample was weighed before and after oven drying at 65°C until mass stabilization (±24 h) to determine bulk density, grain density, and moisture content of the paste corrected for residual salt. For each cuttings sample, we therefore obtain a number of physical attributes of the paste and the pore water salinity estimated from the salt content of the decanted water and porosity results of the cuttings (see the grain/bulk density and porosity results in “Density and porosity” in the “Site C0002” chapter [Strasser et al., 2014b]) to complement the permittivity and loss spectrum.

The end-load probe equipment was calibrated and tested against standard material daily prior to sample measurements. Fixture components were measured to remove their electrical responses from the sample data set. It consisted of a measurement of nondielectric material (silicone), followed by measurement of air surrounding the probe, and then measurement of pure water at room temperature. The ECal module calibration was then tested using standard materials from known basic dielectric response (i.e., no charge dispersion with frequency) such as air (ε′ = 80), Milli-Q water (ε′ = 1), and Teflon (ε′ = 2). If the dielectric response of each standard material was flat over the range of 30 kHz–6 GHz and at the expected dielectric values, the ECal module was calibrated and ready for measurement.

Electrical resistivity (cores)

An Agilent 4294A precision impedance analyzer was employed to determine electrical resistivity from measured impedance. The electrochemical impedance spectrum was acquired from 40 kHz to 10 MHz, and the corresponding magnitude |Z| and phase (θ) of the complex impedance were computed at 2 kHz across the sample in the x-, y-, and z-directions for consolidated cores and only in the x-direction for soft-sediment cores. The 2 kHz frequency was chosen because it is an optimum frequency where no inductance or capacitance occur in the rock (i.e., phase close to 0) and is close to the LWD resistivity frequency for further calibration and comparison. For consolidated cores, electrical resistivity was measured on discrete, cubic samples taken from working halves. The complex impedance was measured by holding the cube between two electrodes, and then electrical resistivity for each direction was computed from measured values and face lengths (L_x, L_y, and L_z). For example, the electrical resistivity in the x-direction (R_x) is

In general, the same cube was used for P-wave and electrical resistivity measurements with a cubic sample (2 cm × 2 cm × 2 cm) cut from the working half. Filter papers were soaked before the test in 35 g/L NaCl solution and placed on the sample faces to ensure coupling between the sample and the stainless steel electrodes. As for the P-wave measurements, the cube was rotated to measure impedance in the x-, y-, and z-directions. The vertical anisotropy (α_T) and horizontal anisotropy (α_l) of electrical resistivity were calculated and expressed as a percentage of the mean (e.g., Shipboard Scientific Party, 2001):

and

where α_x, α_y, and α_z are electrical resistivity in each axial direction.

For soft-sediment cores, the complex impedance (i.e., equivalent resistivity) was measured using the Agilent 4294A analyzer and a four-pin array consisting of four electrodes spaced 7.5 mm apart. The array was inserted into the working half and measured the complex impedance, from which the electrical resistivity is calculated:

where d_r is a constant dependent on the geometry of the electrode array. d_r was determined every 24 h by comparing the measured impedance with an IAPSO standard seawater solution (35 g/L NaCl) of a known electrical impedance.

Ultrasonic P-wave velocity and anisotropy (cores)

P-wave measurements on cubic core samples were conducted along three orthogonal directions for analysis of anisotropy. We took approximately one sample per core section near MAD samples. Cubic samples (~2 cm × 2 cm × 2 cm) were extracted from working halves. Using a diamond blade saw, cubes were cut with faces orthogonal to the x-, y-, and z-axes of the core reference, respectively (Fig. F21). The orientation of the axes is defined as z pointing downward along the core axis, x pointing into the working half normal to the split-core surface, and y left along the split-core face. Faces were ground with sandpaper to improve contact with sonic sensors. The cubes were soaked in 35 g/L NaCl solution for at least 24 h before P-wave measurement.

P-wave velocity was measured on the cube along each axis using a P-wave logger for discrete samples (Geotek LTD London, United Kingdom), which is composed of a sample holder and an electronic console. The sample holder is equipped with P-wave transducers, a laser distance sensor, and a temperature sensor. The electronic console mounts with the operation PC and the electronic units used for generating an electric pulse and amplifying received signals. The transmitter and receiver are a type of piezocomposite transducers for compressional waves (P-wave) with a frequency of 230 kHz.

The wet sample is set between the two piezoelectric transducers and held by two 1.5 kg weights with a force of ~30 N (equivalent to a pressure of 75 kPa) on the contact surfaces. An electric pulse generated by a pulse generator is transformed to the compressional wave by the piezoelectric transducer. The wave propagates through the sample to another piezoelectric transducer which transforms the signal into an output electric pulse. The output signal is amplified, processed through an analog-to-digital converter, and displayed on a PC monitor. Traveltime is picked and logged automatically based on a threshold set by the operators. The length of the P-wave path along the sample is automatically measured at the same time by a laser distance sensor mounted in the apparatus.

Calibrations of traveltime offset and laser distance sensor were conducted daily. The traveltime offset was determined by placing the two piezoelectric transducers in direct contact and measuring traveltime. This setup provided a time offset of ~9.8 µs, which was subtracted from the total traveltime to obtain the real traveltime through each sample. Laser distance calibration was conducted by placing the two electric transducers in direct contact and then separating them using a reference box with a height of 2.5 cm.

P-wave velocities along three directions (V_Px, V_Py, and V_Pz) were simply obtained by dividing the sample length by the real traveltime. Horizontal anisotropy (α₁) and vertical anisotropy (α_T) were calculated by

and

Unconfined compressive strength

For stiffer, more indurated sediment, UCS tests were performed on discrete cuboid samples cut from working-half sections, with approximate dimensional ratios of 1 × 1 × 2, oriented with the x-, y-, and z-axes of the cores. The longer dimension was aligned with the z-axis. These tests provide valuable strength data on samples that are too stiff for analyses with the vane shear or the penetrometer. Care was taken to ensure that the cores were free of defects and the end surfaces of cores were parallel and planar. The samples were placed in a manual hydraulic press (Carver Inc., model 30-12) with a load capacity of 30 tons and aligned so that the load was applied vertically along the cuboid sample axis. In order to measure force, a load cell with a capacity of 300 kN (TEAC Corp., model KR300KN) was placed directly beneath the sample. The sample was manually loaded to failure at a slow rate, and the maximum value registered by the load cell (F_max) was recorded. The UCS of the sample was calculated as

where A is the cross-sectional area of the sample. The reading resolution of the load cell is 10 N.

Shear strength measurements

The shear strength of soft-sediment core working halves was measured with an analog vane shear device (Wkyeham Farrance, model WF23544) and a pocket penetrometer (Geotest E-284B). One measurement per core was taken, with care to avoid disturbed or heterogeneous sediment. Measurements were made with the vane rotation axis and the penetrometer penetration direction aligned with the x-axis of the core.

Undrained shear stress (S_u[vane]) was determined by the torque (T) at failure and a constant (K_v) dependent on the geometry of the vane:

All measurements were made using a vane with a height of 12.7 mm and a blade width of 6.35 mm. Pocket penetrometer measurements provide an estimate of unconfined compressive strength (q_u), which is related to the undrained shear stress (S_{u[penetrometer]}) by

where g is the acceleration due to gravity. Penetrometer measurements are taken by pushing a 6.5 mm diameter cylindrical probe into the working half and recording the penetration resistance.

MSCL-I: photo image logger (archive halves)

Digital images of archive-half cores were acquired by a line-scan camera equipped with three charge-coupled devices. Each charge-coupled device has 2048 arrays. The reflected light from the core surface is split into three channels (red, green, and blue [RGB]) by a beam splitter inside the line-scan camera and detected by the corresponding charge-coupled device. The signals are combined and the digital image is reconstructed. A correction is made for any minor mechanical differences among the charge-coupled device responses. A calibration is conducted before scanning each core to compensate for pixel-to-pixel response variation, uneven lighting, and lens effects. After colors of black (RGB = 0) and white (RGB = 255) are calibrated with an f-stop of f/16, the light is adjusted to have an adequate gray scale of RGB = 137 at an f-stop of f/11. Optical distortion is avoided by precise movement of the camera. Spatial resolution is 100 pixels/cm.

For archive halves from Hole C0021B, image scanning was carried out using the MSCL-S, a GEOTEK product, at KCC. The scanner was calibrated with aperture setting at F6.7 and scanned sections in the same aperture condition. A white chart and grayscale card were scanned as quality control measurements while scanning each section. An image file of this instrument was stored at approximately every 20 cm interval so that a scanned section image was consistent with several image files. After section scanning, each piece was merged into a whole section image. Resolution of the images taken at KCC was 96 dpi, whereas images obtained on the Chikyu were 300 dpi. Merged images were processed by gamma correction at the value of 1.4 using a batch file to change the brightness. This gamma correction value of 1.4 was the same value applied to Expedition 314, 315, 316, 319, 322, 331, and 333 core images in the core descriptions. The images were processed by Adobe Photoshop to adjust RGB values of the grayscale to around 100, 100, and 100, respectively.

MSCL-C: color spectroscopy (archive halves)

A diffuse-reflected spectrophotometer is used to measure core color. The MSCL-C system is an xyz-type aluminum frame equipped with a color spectrophotometer (Konica-Minolta, CM-2600d). Seven core sections can be scanned simultaneously by the sensor unit (including the spectrophotometer and small distance measuring system using a laser sensor). The sensor moves over each section and down at each measurement point to measure the split archive core surface. The reflected light is collected in the color spectrophotometer’s integration sphere and divided into wavelengths at a 10 nm pitch (400–700 nm). The color spectrum is then normalized by the source light of the reflectance and calibrated with the measurement of a pure white standard. The measured color spectrum is normally converted to lightness (L*) and chromaticity variables a* and b* (see Blum [1997] for details). These parameters can provide information on relative changes in bulk material composition that are useful to analyze stratigraphic correlation and lithologic characteristics and cyclicity.

Leak-off test

A leak-off test (LOT) is designed to determine the maximum mud weight to prevent well damage by hydraulic fractures, the least principal stress of the formation, and the faulting modes when vertical stress is known (White et al., 2002; Zoback, 2007). In an LOT, the well is first pressurized by pumping drilling mud into the drill string. Once the pressure reaches a peak, pumping is terminated (shut in). In general, the minimum horizontal stress can be inferred from different points on the pressure record as a function of either time or volume (i.e., leak-off pressure [LOP], instantaneous shut in pressure [ISIP], and fracture closure pressure [FCP]) (White et al., 2002).

Injection of mud into an elastically responding borehole leads to a linear relationship between the injected mud volume and borehole pressure. LOP corresponds to the first deviation of the pressure from the linear increase as a result of fracture initiation. Beyond this point, the gradient of pressure versus injected mud volume (dP/dV) decreases because mud escapes into rock formation (Engelder, 1993). ISIP is defined as the point where the steep pressure decrease after shut in deviates from a straight line, and FCP corresponds to the intersection of two tangents to the instantaneous reduction of pressure and the slow reduction in pressure until bleed off. In general, ISIP is visually easier to determine than FCP and is considered to be the best approximation of least principal stress (Zoback, 2007).

The LOT in Hole C0002F was carried out at the base of the 26 inch hole (872.5 mbsf; 2840 m DRF) after the drill-out cement process below the 20 inch casing shoe, which was set during Expedition 326 (Expedition 326 Scientists, 2011). A 3 m long, 17 inch diameter open hole was drilled into the formation below the cement plug. Two cycles of pressurization were conducted because a large amount of drilling mud was lost and LOP was not clearly defined during the first cycle.

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